The wrong fiber type is selected on the OTDR tab in Setup. A patch cord, launch fiber, or fiber segment has the wrong core size, backscatter coefficient, or mode field diameter. However, like any measurement technique, OTDR. If the pigtail is sufficiently long, 10 meters or so, VIAVI SolutionsTM Optical Time Domain Reflectometers (OTDRs) with pulses as short as 1 foot can perform these measurements. It can verify splice loss, measure length and find faults. The OTDR is also commonly used to create a "picture" of fiber optic cable when it is newly installed. Can someone explain what would. OTDR settings are a balance between dynamic range, acquisition time, spatial resolution and accuracy.